A large number of rodents is grown in the United States for various purposes. Rodents of various sizes are required for different purposes. The animals which are commercially raised and which are relevant to this invention include mice, rats, hamsters, guinea pigs and gerbils. For the purpose of the examples given in the following specification, mice are the rodents in question. The invention is useful with the other animals named and with other similar animals, providing the dimensions are proportionately scaled to the animals' size.
The rodents are raised for various purposes. A large number are raised for medical research. Rodents of various types can be purchased with varying physical and genetic characteristics so that they are useful in medical research and development. Other rodents are grown as food for other animals. For example, mice are the preferred food for many snakes.
The raising of rodents has become quite standardized. A rectangular box or cage with solid sides and solid bottom is used for breeding, growing and supplying laboratory quality rodents, including mice. The typical mouse breeding and initial growing cage has a solid bottom which is 20 inches long by 12 inches wide and has solid walls therearound which are 6 inches high. The mice require bedding for breeding and nesting. Thus, bedding is placed in the cage. The bedding is preferably sterilized byproduct material, such as chopped newspaper or ground bark. One male and four to five female mice are placed in the cage. Food and water are supplied by dispensers to the mice in the cage. Modern rodents are bred for large litters and high growth rates. Consequently, there is an enormous amount of food and water consumed together with the deposit of correspondingly enormous quantities of solid and liquid waste. The accumulation of waste is such that the cage must be cleaned approximately every six days. Otherwise, ammonia levels become too high for the health of the animals. As a result, while the old cage is removed, cleaned and sterilized, the animals must be removed and placed in a new cage with new bedding or, alternatively, removed and held in temporary containers until the old cage has been restored to a habitable condition. This removal of the animals destroys their nesting sites and upsets their routine behavior. Upsetting routine behavior delays their growth and reproduction as well as exposing them to increased physical and health hazards.
The current belief in the industry and art is that rodents cannot be bred in a cage having a screen bottom. This is because the bedding would fall through the screen, and the females would not breed unless they have nesting opportunity. Furthermore, if they did give birth in the screen bottom cage, the infants would fall through the screen bottom and be lost. For these reasons, the industry requires solid bottom cages for the breeding, gestating, birthing and initial growing of such animals, including rats and mice, and then uses all-screen bottom cages for adult rodents only.
In order to maintain health, the cages must be cleaned and sterilized before reuse. In addition, new sterile bedding or recycled sterile bedding must be supplied. The handling, removal and return of the animals and the cleaning and reusing of the old cage is very labor-intensive because it must be performed regularly, about every six days, in accordance with present practice. Accordingly, there is a need for a system which provides sufficiently clean living conditions for the rodents, together with a reduced amount of maintenance labor.